The present application relates to measurement techniques for characterizing the response of a liquid crystal display.
With liquid crystal display's advantage on size, weight, style, power consumption and/or modulation transfer function in comparison to many other display technologies, the liquid crystal based displays are more commonly being used for displaying video, such as television broadcasts. Liquid crystal displays compared with traditional cathode ray tube and plasma displays, however, tend to have a significant shortcoming related to motion blur of moving images. One of the principal reasons for motion blur in a liquid crystal panel is that the panel has a relatively slow temporal response in comparison to the frame rate of typical video. Significant effort has been made to accelerate the liquid crystal panel's temporal response, and one of these techniques is generally referred to as overdrive technology. To measure the response of the liquid crystal panels a response time may be used.
Response time is typically defined as the arrival time at 90% of the difference between the starting luminance and the targeted luminance. The concept of response time for liquid crystal displays was historically developed to describe the characteristics of on-off black-white liquid crystal panels. To describe liquid crystal panels with gray-level capability, a set of response times (typically 9×9) that sample and cover the range of driving values are measured and are typically represented by three dimensional bar graphs. It has been noted that the definition of response time gives larger error tolerance to the transitions with larger difference between starting and targeted luminance. For example, response time from 0 to 255 is measured at the time when the actual luminance reaches 229.5, while response time from 200 to 255 is measured at the time when the actual luminance reaches 249.5. Although the two transitions seemingly share the same target luminance, the actual response times are actually measured at different ending luminance values (249.5 and 229.5 respectively).
A metric for moving picture response time (MPRT), has been developed by an industrial working group. MPRT is based on measuring the blurred width of camera-captured moving sharp edges on the screen of a display device. The camera imitates the human visual system (HVS) with smooth pursuit and integration effects. Therefore, MPRT can be used not only to describe LC panels, but also to perform comparisons with PDP and CRT as well. However, MPRT is not a desirable metric for quantitatively describing the temporal response of a liquid crystal panel. Most importantly, MPRT mixes together the two blurring factors of a liquid crystal panel: its hold-type display and its slow temporal response. Also, obtaining a MPRT measurement is complicated. To effectively obtain a MPRT measurement the system needs to mimic the two effects in the human visual system, namely, smooth pursuit and integration. While integration may only require properly setting the camera's exposure time, smooth pursuit tends to require that the camera chases the motion of sharp edges. Due to implementation difficulty of smooth pursuit, as many as four different methods have been developed. Two of them make the camera lens physically pursue the moving object (e.g., common pursuit). Because the camera pursuit tends to be expensive, the other two simpler methods calculate the results from still camera lens plus mathematical models of pursuit and integration effects.